In a recent wiring technology, copper lines are replacing aluminum lines to improve performance of a semiconductor device. In a manufacturing process of the semiconductor device, a technology for forming a copper film on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) is important. A chemical vapor deposition method (hereinafter, referred to as “CVD”) using a copper organic compound as a material has been known as one of technologies for forming a copper film on the wafer.
When a copper film is formed on the wafer having an interlayer insulating film (hereinafter, referred to as an “insulating film”) by using CVD, a copper organic compound, e.g., Cu(hexafluoroacetylacetonate)trimethylvinylsilane (hereinafter, referred to as “Cu(hfac)TMVS”) serving as a source gas is supplied to a processing chamber in a vacuum state, and the Cu(hfac)TMVS is thermally decomposed on the heated wafer to form the copper film on a surface of the insulating film. However, since copper atoms tend to be diffused into the insulating film, the copper film is formed on a diffusion barrier film (hereinafter, referred to as a “base film”) called a barrier metal, which is formed in advance on the insulating film, instead of being directly formed on the insulating film. The base film employs titanium, tantalum or the like, and the barrier metal reacts with an organic material from the copper organic compound, thereby producing organic impurities at an interface between the copper film and the barrier metal.
If the copper film is grown on an organic impurity layer, adhesiveness between the base film and the copper film is weakened and a resistance between an upper copper line and a lower copper line increases. Accordingly, electrical characteristics deteriorate or the copper film is peeled off while processing the wafer, resulting in a reduction in production yield. Further, since the organic impurity layer has poorer wettability than the base film, copper can be easily aggregated to thereby reduce buriability of the copper in a trench having a high aspect ratio, thereby causing a defect of the copper line.
Meanwhile, a low-k material of a low dielectric constant is used as the insulating film for a higher speed operation in a semiconductor device. The insulating film is formed of a porous material, such as a material containing silicon, oxygen and carbon (hereinafter, referred to as “SiOC”), of a low dielectric constant. However, the insulating film made of a porous material easily absorbs water from the atmosphere, and discharges the water into the base film after the base film is coated on the surface of the insulating film.
Regarding such a phenomenon, the present inventors have a following conjecture. That is, the above-mentioned titanium and tantalum belong to a group of valve metals, and an oxide layer called a passivation film is formed on a contact surface with the insulating film to prevent water from passing therethrough. Accordingly, when a valve metal is used as the base film, although water is discharged from the insulating film, movement of the water is prevented by the passivation film formed on the contact surface with the insulating film. Thus, it is possible to prevent an oxide layer of poor adhesiveness to the copper film from being formed at the interface in contact with the copper film.
Therefore, the inventors have conducted an investigation on the use of titanium nitride or titanium carbide (nitride or carbide of a valve metal) for the base film of the copper film in order to solve a problem of formation of the organic impurity layer while maintaining advantages of the valve metal. However, when the above-mentioned materials are used as the base film, the passivation film formation is insufficient although it is possible to prevent formation of the organic impurity layer.
Further, Patent Document 1 discloses a method for forming a copper film for copper lines after nitride of titanium or tantalum is coated on the surface of the insulating film, but does not deal with the above-mentioned problem.
Patent Document 1: Japanese Laid-open Publication No. 2000-299296: claim 14